1. Field of the Invention
The present invention generally relates to an apparatus and method for automatically and periodically introducing a fluid into a producing oil well. The present invention is particularly useful in a production string where it provides a convenient apparatus and method for routinely, automatically and periodically draining production fluid from the string in order to permit regular injection of chemicals into the producing formation or injection of solvents or hot fluid to dissolve paraffin deposited in the production tubing. More particularly, the present invention relates to an apparatus and method employing a tubing drain valve actuated to its open position by application of a force developed across a movable piston by the pressure in the interior of the production string coupled with positive closing by mechanical means, together with sensing and actuating devices to permit regular, periodic and automatic injection of fluid into a producing well.
2. Description of the Background
It is often desirable to have a drain valve located in the wall of a borehole tubing string. It is particularly desirable to have a tubing drain valve located in a production string for a variety of reasons. For example, the efficiency of production strings is often decreased by the deposit of paraffin, wax and similar substances on the interior of the string as the string rises through lower temperature zones from a deep, high temperature production zone. It is necessary to remove these deposits in order to maintain the efficiency of the production string. Ideally, an automated and prescheduled treating before production is adversely affected would be desirable.
Present methods for removing such deposits employ hot oil, water or steam which is generally forced down the annulus between the production string and the borehole casing. The hot oil, water or steam enters the production string through the downhole pump and returns to the surface through the string where the elevated fluid temperature slowly dissolves the deposits. Because of the long and circuitous path to the zone of interest, fluid reaching the zone of interest is often at a temperature significantly lower than the injected fluid. It is often desirable to inject the producing zone with a variety of chemicals to increase or aid production. These chemicals also are injected by the previously described method for injecting hot oil, steam or hot water. These methods suffer from the disadvantage that excessive quantities of fluids and chemicals are required because the injection is indirect through the annulus. Alternatively, dedicated, small diameter injection tubing is employed to directly inject chemicals into the production zone. Systems for carrying out the above processes must be performed by field personnel on a routine or as needed basis.
In an attempt to solve some of the above problems, others have proposed a variety of valves suitable for use in a borehole production string. For example, valves which open when the pressure within the tubing exceeds a pre-determined pressure have been proposed. Such valves permit fluid communication between the interior of the production string and the annulus at the valve location. These valves are useful for draining the production fluid above the valve location and for injecting chemicals into the borehole at the valve location only if the valve remains open after its initial opening. It is still necessary to pull the production string in order to close these valves. Accordingly, these valves are of no value in the assembly of an automatic treating system. Alternatively, other check valves, e.g., spring loaded valves, operable above a predetermined pressure permit injection of fluids into a borehole at the valve location, but fail to provide a means for draining fluid from the production string.
Accordingly, there has been a long felt but unfulfilled need within the industry for an apparatus and method for automatically introducing a fluid into a producing well. Such a system would require a tubing drain valve which is both opened and closed automatically and reliably from the surface. This valve must also be easily maintained in the open position in order to permit drainage of the production string. Further, this valve must be positively closable from the surface to permit resumption of production.